document代表整个文档
<!DOCTYPE html>
<html>
<head>
	<title></title>
</head>
<body>
	<div id='only'>123</div>
	<div name = 'only'>234</div>
	<div class="demo"></div>

	<div>
		<span>
			<strong class="demo">123</strong>
		</span>
	</div>
	<input type="" name="furit">
	<script type="text/javascript">
		var div = document.getElementById('only');//在Ie8一下，id不区分大小写,name为 'only'可以选出来
		var div1 = document.getElementsByTagName("div");//把所有属性，拿出以类数组展示
		console.log(div1);
		var div2 = document.getElementsByClassName('demo');
		console.log(div2);

		var inp = document.getElementsByName('furit');//注意只有部分name可生效，表单，表单元素
		console.log(inp);

		var strong = document.querySelector('div > span > strong.demo');
		var strong1 = document.querySelectorAll('div > span > strong.demo');//选出来的是一组
		console.log(strong);
		console.log(strong1);


		var newDiv = document.createElement('div');
		document.body.appendChild(newDiv);
		

	</script>
</body>
</html>